1. Field of the Invention
The present invention relates to liquid crystal display device of a passive matrix type and an active matrix type. Particularly, the invention relates to an electrode structure of transflective type liquid crystal display device having both functions of a transmission type and a reflection type.
2. Description of the Related Art
In recent years, by explosive spread of a portable information terminal represented by a portable telephone, there is needed a display capable of dealing with light-weighted formation, conservation of power consumption and a change in an environment of use.
Further, in view of thin film formation and light-weighted formation, a liquid crystal display device or an organic EL display device is representatively promising.
Power consumption of a transmission type display device is inconsiderable for driving only a display. However, a liquid crystal per se does not emit light and therefore, a back light is needed for displaying as a display. For use of a portable telephone, an EL back light is generally used, however, power is separately needed for the back light and a characteristic of conservation of power consumption particularly to a liquid crystal is not fully utilized, which is disadvantageous in conservation of power consumption. Further, although in a dark environment, display of a display is viewed with excellent contrast, in an ordinary bright environment, the display is not viewed so well and there is a drawback in adaptability in accordance with the environment of use both in cases of an upper emitting type and a lower emitting type.
Further, the organic EL display device is characterized in that a display element per se emits light. Although power consumption thereof becomes larger than that of a reflection type liquid crystal display device, the power consumption is smaller than that of a transmission type liquid crystal display device (having back light). However, similar to the case of the transmission type liquid crystal display device, although in a dark environment, display of a display is viewed excellently, in an ordinary bright environment, the display is not viewed so well and therefore, there is still a drawback in adaptability in accordance with an environment of use both in cases of the upper emitting type and the lower emitting type.
Further, the reflection type liquid crystal display device utilizes outside light from an environment as light for display. On the side of the display, the back light is not basically needed, only power for driving a liquid crystal and a drive circuit is needed and therefore, positive conservation of power consumption is achieved. Further, quite contrary to the former two, although in a bright environment, display of a display is viewed excellently, in a dark environment, the display is not viewed so well. Considering the use of a portable information terminal, the portable information terminal is mainly used outdoors and there is frequently a case of viewing the display in a comparatively bright environment, however, this is still insufficient in terms of adaptability in accordance with an environment of use. Therefore, locally, a reflection type display device integrated with a front light is on sale such that the display can be carried out even in a dark environment.
Hence, attention is given to a transflective type liquid crystal display having advantages of both of a transmission type and a reflection type liquid crystal display device by combining the device. In a bright environment, a characteristic of the reflection type of conservation of power consumption and excellence in optical recognizing performance under the environment is utilized, meanwhile, in a dark environment, a characteristic of excellence in contrast provided to the transmission type is utilized by using a back light.
A transflective type liquid crystal display device is disclosed in JP11-101992. The device is a reflection and transmission type (transflective type) liquid crystal display device having a constitution which can be used as the reflection and transmission type liquid crystal display device in which by fabricating a reflecting portion for reflecting outside light and a transmitting portion for transmitting light from a back light to include in a single display panel, when a surrounding is totally dark, display is carried out by utilizing light transmitting through the transmitting portion from the back light and light reflected by the reflecting portion formed by a film having comparatively high reflectance and as a reflection type liquid crystal display device in which when outside light is bright, display is carried out by utilizing light reflected by the reflecting portion formed by the film having the comparatively high optical reflectance.
Further, the above-described transflective type liquid crystal display device is provided with a special uneven structure having optical diffusion performance particularly at the reflecting portion for carrying out display by reflection. Because a reflection electrode reflects light incident on a surface from a certain direction by a certain angle of incidence only to a location having a specific angle of emittance in a specific direction (Snell's law) in view of the structure and therefore, when the surface is flat, a direction and an angle of emitting light are determined to be constant relative to incidence of light. When a display is fabricated under such a state, a display having very poor optical recognizing performance is brought about.
The transflective type liquid crystal display device may be regarded as a display in corresponding well with a special condition of use of a portable information terminal. Particularly, in use thereof for a portable telephone, considerable demand is anticipated to promise in the future. Hence, in order to ensure stable demand or to meet enormous demand, there is apparently a need of achieving further reduction in cost.
However, in order to form the uneven structure shown above, there is needed a method of attaching an uneven shape at a layer below a reflection electrode and thereafter forming the reflection electrode thereabove.
Further, regardless of the above-described example, in order to fabricate a transflective type liquid crystal display device, patterning operation is needed for forming an uneven structure at either or both surfaces of a reflection electrode and a transmission electrode constituting a pixel electrode or at a layer below a pixel electrode and therefore, a number of steps is increased. An increase in the number of steps brings about a disadvantageous situation of a reduction in yield, extension in process time, or an increase in cost.